package expr

import (
	"context"

	"github.com/grafana/grafana-plugin-sdk-go/backend"

	"github.com/grafana/grafana/pkg/components/simplejson"
	"github.com/grafana/grafana/pkg/plugins"
	"github.com/grafana/grafana/pkg/services/datasources"
	"github.com/grafana/grafana/pkg/setting"
)

// DatasourceType is the string constant used as the datasource when the property is in Datasource.Type.
// Type in requests is used to identify what type of data source plugin the request belongs to.
const DatasourceType = "__expr__"

// DatasourceUID is the string constant used as the datasource name in requests
// to identify it as an expression command when use in Datasource.UID.
const DatasourceUID = DatasourceType

// DatasourceID is the fake datasource id used in requests to identify it as an
// expression command.
const DatasourceID = -100

// OldDatasourceUID is the datasource uid used in requests to identify it as an
// expression command. It goes with the query root level datasourceUID property. It was accidentally
// set to the Id and is now kept for backwards compatibility. The newer Datasource.UID property
// should be used instead and should be set to "__expr__".
const OldDatasourceUID = "-100"

// IsDataSource checks if the uid points to an expression query
func IsDataSource(uid string) bool {
	return uid == DatasourceUID || uid == OldDatasourceUID
}

// Service is service representation for expression handling.
type Service struct {
	cfg               *setting.Cfg
	dataService       backend.QueryDataHandler
	dataSourceService datasources.DataSourceService
}

func ProvideService(cfg *setting.Cfg, pluginClient plugins.Client, dataSourceService datasources.DataSourceService) *Service {
	return &Service{
		cfg:               cfg,
		dataService:       pluginClient,
		dataSourceService: dataSourceService,
	}
}

func (s *Service) isDisabled() bool {
	if s.cfg == nil {
		return true
	}
	return !s.cfg.ExpressionsEnabled
}

// BuildPipeline builds a pipeline from a request.
func (s *Service) BuildPipeline(req *Request) (DataPipeline, error) {
	return s.buildPipeline(req)
}

// ExecutePipeline executes an expression pipeline and returns all the results.
func (s *Service) ExecutePipeline(ctx context.Context, pipeline DataPipeline) (*backend.QueryDataResponse, error) {
	res := backend.NewQueryDataResponse()
	vars, err := pipeline.execute(ctx, s)
	if err != nil {
		return nil, err
	}
	for refID, val := range vars {
		res.Responses[refID] = backend.DataResponse{
			Frames: val.Values.AsDataFrames(refID),
		}
	}
	return res, nil
}

func DataSourceModel() *datasources.DataSource {
	return &datasources.DataSource{
		Id:             DatasourceID,
		Uid:            DatasourceUID,
		Name:           DatasourceUID,
		Type:           DatasourceType,
		JsonData:       simplejson.New(),
		SecureJsonData: make(map[string][]byte),
	}
}